This invention relates to in-line valves and particularly to means for balancing the valves so as to reduce or minimize the pressure loading thereon.
This invention constitutes an improvement over the ejector disclosed in U.S. patent application Ser. No. 149,134 filed one June 2, 1971 now Pat. No. 3,721,387 entitled "Ejector With Variable Mixing Section and Primary Nozzle Areas" by George E. Wilmot, Jr. and assigned to the same assignee. As shown in this patent application surpra the plug moves relative to the primary nozzle of the ejector in order to vary its area. The problem encountered with this type of ejector plug and construction is that when the plug moves open relative to the ejector nozzle the integrated pressure force acting on the upstream side of the plug evidences a sudden and relatively large reduction in force which adversely affects the actuator that positions the plug.
I have found that I can eliminate or minimize the change of net force caused by the pressures acting on the plug and hence obviate the problem of the sudden drop in force by incorporating a series of discretely located aperatures in the hollow plug so spaced as to permit air to flow in and out thereof for creating an internal pressure and hence a force which force balances the force created by the integrated pressure acting on the upstream portion of the plug. Thus, as the plug is moved to open or close the adjacent nozzle opening the pressure in the balanced chamber changes similarly to the integrated pressure acting on the upstream side of the plug so that the net force change on the plug is zero, or substantially zero. This is accomplished by virtue of the fact that the location of the holes are at such intervals that the varying external pressure distribution will cause the balance pressure to be equal to the integrated pressure distribution at all plug positions. In this manner the uniquely placed holes serves to obtain a balanced pressure to match the pressure versus flow characteristics desired, and since the balanced pressure obtained is a function of the magnitude of the inlet pressure the ratio of the integrated pressure and balance pressure remains constant notwithstanding changes of the inlet pressure.